730 A MANUAL OF PHYSIOLOGY 



organ especially concerned in the co-ordination of move- 

 ments and the maintenance of equilibrium, supporting his 

 conclusions by an elaborate series of experiments. Not- 

 withstanding the very large amount of experimental and 

 clinical study which has been devoted to the cerebellum 

 since the time of Flourens, our knowledge of its functions 

 has hardly advanced beyond the point then reached. 

 Indeed, it may be said that the tendency has been rather 

 to abridge than to extend the field of current physiological 

 doctrine on this subject. For while it has been shown that 

 the integrity of the cerebellum is essential to equilibration, it 

 is by no means certain that it is essential for the co-ordination 

 of movements other than those concerned in the maintenance 

 of equilibrium and in locomotion. Animals entirely deprived 

 of the cerebellum have shown, after the primary effects of 

 the operation have passed away, no impairment in general 

 co-ordinative power ; and cases are on record in which the 

 human cerebellum has been found at death to be utterly 

 disorganized, and yet in which many classes of movements 

 have been well co-ordinated during life. But what has been 

 noticed in such cases is a marked inability to maintain the 

 upright posture, a staggering gait, twitching movements of 

 the eyes (nystagmus) in a word, a general disorder of the 

 mechanism of equilibration. In cases of congenital defect 

 of the cerebellum, the power of walking, and even of 

 standing, is late in being acquired, and usually imperfect. 

 The connections of the cerebellum with other parts of the 

 central nervous system and with the periphery corroborate 

 the direct results of experiment. For the most important 

 afferent impulses concerned in equilibration are those from 

 the muscles, the skin, the semicircular canals and vestibule 

 of the internal ear, and the eyes. And the cerebellum, as 

 we have seen (p. 689), is linked with all of these, and has 

 besides an extensive crossed connection through the middle 

 and superior peduncles with the opposite cerebral hemi- 

 sphere. The importance and extent of this crossed connec- 

 tion with the great brain is illustrated by the facts that in 

 disease atrophy or deficient development of one cerebellar 

 hemisphere is associated with a similar condition of the 



